Photocatalyst water treating apparatus

ABSTRACT

A photocatalytic water-processing system decomposes organic and inorganic materials present in water. The system includes a reservoir for storing the water to be processed, a main unit formed separately and connected to the reservoir, an inlet pipe for guiding the water from the reservoir to the main unit, an outlet pipe for returning the water to the reservoir, and a pump for guiding the water from the reservoir to the main unit and returning the water. The reservoir has an electrode unit therein for electrolyzing the water so as to flocculate and precipitate the inorganic materials in the reservoir, and a filter is arranged within the main unit. Also, a photocatalytic processing device is arranged within the main unit at a downstream side of the filter for decomposing the organic material in the absence of scale formed of the inorganic materials.

CROSS TRFERENCE TO RELATED APPLICATION

The present application is based on International Application No.PCT/JP2004/004039 filed on Mar. 24, 2004.

TECHNICAL FIELD

The present invention relates to a photocatalytic water-processingsystem that utilizes a reservoir where water that requires processing,such as industrial circulating water, is temporarily stored andinorganic materials present in the water are decomposed by electrolysis.In particular, the present invention relates to a photocatalyticwater-processing system in which rust deposits and scale of silica,magnesium and other inorganic compounds formed in the reservoir or thepiping or over the UV-lamp of the system are decomposed and removed byelectrolysis without using any chemicals.

BACKGROUND ART

Criteria for the maintenance and improvement of water quality have beenseriously reviewed recently, and there is an increasing need for moresophisticated water-processing technologies that ensure sufficient waterquality. In particular, development of water-processing technologies forremoving environmental hormones, such as dioxin, organochlorinecompounds, such as trihalomethane, and harmful bacteria, such asLegionella and E. coli, is an urgent task.

The criteria for the prevention of Legionella infection specify that,should the number of detected bacteria of genus legionella above 10²CFU/100 ml in environmental water (such as cooling tower water) thatresidents are less likely to inhale the aerosol of, immediate measures,such as cleaning, be taken to reduce the number of bacteria.

The criteria also specify that the bacterial count must be kept lessthan 10 CFU/ml for the water for use in bathtub or shower that residentsare likely to directly inhale the aerosol of.

On the other hand, clogging of the piping caused by scale deposits ofinorganic compounds and metal corrosion has posed a serious problem, andthere has been a great need in various industries for the development ofnew water-processing technologies to decompose and remove thesematerials.

Some of the conventional water-processing systems use photocatalysts.These conventional photocatalytic water-processing systems operate bytaking advantage of photocatalytic activity of photocatalysts, such astitanium dioxide, that occurs as the catalysts are irradiated with UVrays in the water that requires processing.

One example of such systems is a fluid-processing system equipped withozone-generating means and photocatalyst means. In this system, ozone isgenerated in the medium, or the water to be processed. Once the ozone isgenerated, a photocatalyst and the ozone are together exposed to UVrays, so that the ozone is decomposed by the catalyst and free radicalsthat can destroy contaminants are obtained (See, Patent Article 1).

A water-processing process is also proposed, as is a system for theprocess. This process involves a photocatalytic process in conjunctionwith an ozone process and processes organic materials in water to beprocessed into inorganic products (See, Patent Article 2).

All of the conventional photocatalytic water-processing technologiesface the same problem, however. A long term use of the system results inthe deposition of scale and oil on the silica glass jacket of theUV-lamp, decreasing the UV transmittance. The resulting decrease in theUV-lamp performance makes the long-term, stable processing of waterdifficult.

As a different approach, a water-processing system is also known thatsterilizes water by electrochemically decomposing contaminants. In onesuch system, water in an electrolysis tank is oscillated andelectrolysis is carried out to remove, or prevent the deposition of,scale deposits on the surface of the electrodes placed in theelectrolysis tank. This system facilitates maintenance of theelectrolysis tank (See, Patent Article 3).

However, this type of water-processing system requires some means forgenerating oscillation, such as means for generating bubbles or meansfor sonicating water provided within the electrolysis tank.

Another approach is to process water with chemicals. One such system isused in food processing plants to process waste water. This wastewater-purification system includes a chemical processing unit in whichpH is adjusted, flocculation is performed using chemicals, and wasteparticles grow and precipitate (See, Patent Article 4).

However, chemicals used in this type of water-processing system todecompose and remove COD and BOD components, hexane extracts, totalphosphorus, and total nitrogen present in waste water requires areaction tank for processing. In addition, the running cost of thissystem is high.

(Patent Article 1: Japanese Translation of PCT International ApplicationNo. Hei 10-511572)

(Patent Article 2: Japanese Patent Laid-Open Publication No. 2000-5747)

(Patent Article 3: Japanese Patent Laid-Open Publication No. 2003-24943)

(Patent Article 4: Japanese Patent Laid-Open Publication No.2000-279995)

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a photocatalyticwater-processing system that allows unprecedented water-processing inwhich rust deposits and scale of silica, magnesium and other inorganiccompounds formed in the reservoir of the system, in which to store waterthat requires processing (e.g., industrial circulating water), or in thepiping, or over the UV-lamp jacket of the system, are dissolved andremoved without using any chemicals.

Accordingly, a first construction of the present invention is aphotocatalytic water-processing system utilizing a reservoir in whichwater that requires processing is temporarily stored and in whichorganic and inorganic materials present in the water are decomposed, thesystem comprising:

a circulation path including:

-   -   a main unit arranged outside the reservoir in such a manner that        the water that requires processing flows therethrough;    -   an inlet pipe connecting the reservoir to an inlet of the main        unit; and    -   an outlet pipe connecting an outlet of the main unit to the        reservoir;

a pump for circulating the water through the circulation path;

a filter arranged within the main unit;

photocatalytic processing means arranged within the main unit downstreamof the filter and including a photocatalyst carrier and a UV-lamp; and

an electrode unit arranged within the reservoir, wherein the water iselectrolyzed as a current is applied to the electrode unit.

According to the first construction of the present invention, the waterthat requires processing is temporarily stored in the reservoir, whereit is subjected to electrolysis by the electrode unit. The water is thenforced by the pump into the main unit, where it is filtered through thefilter and is then processed by the photocyatalytic processing meanslocated downstream. These processes are repeated as the water circulatesthrough the circulation path.

As the water is electrolyzed in the electrode unit, inorganic compoundsresulting from the water are dissolved and peeled off, and flocculatedand precipitated, and removed. As a result, deposition of scale in thecirculation path is prevented.

The processing of water by photocatalyst in combination withelectrolysis provides synergistic effects: Such combined processing cansubstantially remove the rust and the scale of calcium, magnesium andother inorganic compounds formed over the jacket of UV-lamps, which canpose a significant problem in the conventional water-processing byphotocatalysts alone. This processing technique thus allows highlyeffective processing of water. The technique also facilitates themaintenance of the system and minimizes the reduction in thetransmittance of UV-lamp jackets, thus making long-term, stablewater-processing and reduction in the time and labor required in themaintenance possible. For example, it is not necessary to manuallyremove the scale on a regular basis by taking off the UV-lamps eachtime.

A second construction of the present invention is characterized in thatin the first construction, the electrode unit includes at least twoelectrodes formed of any one or two or more of zinc, a magnesium alloy,copper, iron, stainless steel, a titanium alloy, an aluminum alloy, andplatinum.

A third construction of the present invention is characterized in thatin the first or the second construction, the electrode unit comprises aplatinum-plated titanium alloy.

A fourth construction of the present invention is characterized in thatin any one of the first to the third construction, the filter comprisesany one of porous oxide ceramics, aluminum oxide, synthetic resin fiber,paper, stainless steel, and activated carbon.

A fifth construction of the present invention is characterized in thatin any one of the first to the fourth construction, the UV-lamp emitsradiation with a spectrum ranging from 180 to 400 nm.

A sixth construction of the present invention is characterized in thatin any one of the first to the fifth construction, the photocatalystcarrier comprises any one of noble metal, titanium dioxide, aluminumoxide, silicon oxide, and a mixture thereof.

A seventh construction of the present invention is characterized in thatin any one of the first to the sixth construction, the water thatrequires processing comprises at least one selected from industrialcirculating water, industrial waste water, tap water, sewage, soil andunderground water, pond water, swimming pool water, and domestic wastewater.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a photocatalyticwater-processing system representing one embodiment of the presentinvention.

FIG. 2 is a diagram of an electric circuit representing the electrodeunit of the photocatalytic water-processing system.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will now be described in detailwith reference to the accompanying drawings.

(Overall Construction of the Photocatalytic Water-Processing System)

Referring first to FIG. 1, the overall construction of a photocatalyticwater-processing system of the present invention is described. FIG. 1 isa schematic cross-sectional view of a photocatalytic water-processingsystem 1 representing one embodiment of the present invention. In thisembodiment, water 100 to be processed by the photocatalyticwater-processing system 1 is industrial circulating water.

The photocatalytic water-processing system 1 in this embodiment utilizesa reservoir 11 arranged in a cooling tower in a factory for coolingindustrial circulating water. Specifically, the system includes twocirculation paths: a first circulation path that runs through thefactory for circulating the circulating water 100 (not shown), and asecond circulation path in which the photocatalytic water-processingsystem 1 is arranged. The reservoir 11 is arranged between the twocirculation paths. The water 100 is circulated through the firstcirculation path for industrial use and flows out the first circulationpath, through a water inlet 12, into the reservoir 11 where it istemporarily stored.

The photocatalytic water-processing system 1 is arranged in the secondcirculation path including the reservoir 11 in such a manner that it isinserted and connected to the reservoir 11. In this manner, the water100 stored in the reservoir 11 is processed in multiple steps todecompose organic and inorganic materials (which will be describedbelow) as it circulates through the second circulation path.

As shown in FIG. 1, the second circulation path consists of thereservoir 11, a main unit 2 arranged outside the reservoir 11 so thatthe water flows through it, an inlet pipe 8 connecting the reservoir 11to the inlet of the main unit 2, and an outlet pipe 9 connecting theoutlet of the main unit 2 to the reservoir 11.

After processed in the photocatalytic water-processing system 1, thewater 100 flows back into the first circulation path via a water outlet13 connected to the reservoir 11 and is again used as circulation water.The water 100 supplied to the first circulation path is used andcirculated as industrial water for a certain period of time and thenflows back through the inlet pipe 12 into the reservoir 11 where it isstored and processed by the photocatalytic water-processing system 1 inthe same manner. After processing, the water flows through the outletpipe 13 out into the first circulation path 13.

As shown in FIG. 1, the photocatalytic water-processing system 1includes the main unit 2, which has the inlet pipe 8 through which thewater flows from the reservoir 11 into the main unit 2 and the outletpipe 9 through which the water flows back into the reservoir 11, afilter 5 for filtering the water that has flowed into the main unit 2, aset of UV-lamps 6 and photocatalyst carriers 7 for carrying out thephotocatalytic reaction to process the water in the main unit 2, a pump4, which is arranged separately from the main unit 2 and forces thewater from the reservoir 11 into the inlet pipe 8, and an electrode unit3 for electrolyzing the water. Thus, in the photocatalyticwater-processing system 1, the electrode unit 3, the pump 4 and the mainunit 2 are individually arranged from upstream. The filter 5, the set ofthe UV-lamps 6 and the photocatalyst carriers 7 are arranged within themain unit 2 in this order with the filter 5 most proximal to the inletside 101 of the main unit 2.

The photocatalytic water-processing system 1 also includes an externalpower source unit 10, which includes a control panel (not shown) thatserves to control the UV-lamps 6, control the amount of current thatflows through the electrode unit 3 and protect the electrode unit 3 fromexcessive current, and control the electric system of the pump 4. Theelectrode unit 3, the pump 4, and the UV-lamps 6 are each activated byturning on power switches provided in the control panel. The powersource unit 10 supplies electricity to the electrode unit 3, the pump 4,and the UV-lamps 6. The power source unit 10 supplies electricity atleast to the electrode unit 3 upon activation of the system.

The power source unit 10 also serves to control the power output to thepump 4 and comprises inverter control means to control the output of thepump 4.

The main unit 2 of the photocatalytic water-processing system 1 isessentially a casing having the inlet pipe 8 for water intake and theoutlet pipe 9 for water discharge, and is arranged separately from thepump 4 and the electrode unit 3. The power lines of the electrode unit3, the pump 4, and the respective UV-lamps 6 are each connected to thepower source unit 10, and their control panels are provided in theexternal power source unit 10.

The electrode unit 3 includes a pair of electrodes 3A and 3B, anelectrode cover 30 that encases the electrodes 3A and 3B, and a DC powersource 31, resistors 32 and 33 and a capacitor 34 which will bedescribed later with reference to FIG. 2. The electrodes 3A and 3B andthe electrode cover 30 are accommodated in the reservoir 11. Theelectrode unit 3 is detachably secured by fastening screws and boltswith the pair of electrodes 3A and 3B held close to each other.

The electrodes 3A and 3B of the electrode unit 3 may be formed of zinc,a magnesium alloy, copper, iron, stainless steel, a titanium alloy, analuminum alloy, or platinum. Although any of these metals may be used inthe electrodes to provide a decreased oxidation-reduction potential, theeffect is particularly significant when platinum-plated titanium alloysare used. The electrodes may be formed as plates, rods, or cylinders.The electrode unit may include two or more electrodes.

The electrode cover 30 serves to secure the electrodes 3A and 3B andprotect them from damages caused by their colliding with each other. Theelectrode cover 30 also serves to prevent deposition of scale on theelectrodes 3A and 3B.

Specifically, the electrode cover 30 has a generally cylindrical shapewith a meshed surface and is inserted vertically into the reservoir 11,so that it covers the electrodes 3A and 3B along the length. Thus, theelectrode cover 30 is preferably made of an insulator that is insulatedfrom the electrodes 3A and 3B at least on its surface. One preferredmaterial of the electrode cover 30 is a synthetic resin.

However, the electrode cover 30 may be grounded in such a manner that itis not electrically connected to the electrode 3A or 3B. In this manner,the electric cover 30 itself functions as a cathode that collects scaleand, thus, reduces the deposition of scale on the UV-lamps 6 arrangeddownstream. In such a case, the electrode cover 30 is preferably made ofa metal, in particular, stainless steel, titanium or other metals thatare highly resistant to rust. When the electrode cover 30 is made of ametal, it is preferably coated with a coating material to form aninsulation layer on the surface where insulation from the electrodes 3Aand 3B is required.

The pump 4 is equipped with a not-shown motor and a not-shown rotaryvane to circulate the water 100 through the second circulation path. Forexample, the pump 4 operates to suction the water in the reservoir 11and discharge it into the inlet side 101 of the main unit 2.

By manipulating the flow control button on the control panel (notshown), the power of the motor of the pump 4 can be controlled toregulate the water flow from the reservoir 11 through the inlet pipe 8into the main unit 2. The pump 4 may be any pump that can providesufficient energy to force the water through the water circulation path.While the pump 4 is placed in the reservoir 11 in this embodiment, itmay be arranged in the midway of the pipe that connects the reservoir 11to the main unit 2.

The filter 5 serves to filter the water to remove solid material andorganic materials. It has a planar structure with generally the samediameter as the inner diameter of the main unit 2 and is secured to theinner wall of the main unit 2 on the periphery. The filter 5 hasnumerous pores, so that solid materials and organic materials present inthe water that are larger than the pore size are removed as the waterpasses through the filter. The filter 5 is made of materials such asporous oxide ceramics, aluminum oxides, synthetic resin fibers, paper,stainless steel, and activated carbon. The synthetic resin fiber ispreferably a nonwoven fabric formed of polypropylene fibers. The poresof the filter 5 are preferably sized 60 to 200 meshes, and morepreferably 120 to 160 meshes.

As shown in FIG. 1, the photocatalytic water-processing system 1includes a plural UV-lamps 6 and a plural photocatalyst carriers 7arranged within the main unit 2 on the water-discharging side 102. TheUV-lamps 6 and the photocatalyst carriers 7 are arranged alternately andare equally spaced apart and opposed to one another. While the UV-lamps6 and the photocatalyst carriers 7 are arranged parallel to the waterflow in the example shown, they may be arranged perpendicular to theflow.

The UV-lamps 6 and the photocatalyst carriers 7 are preferably arrangedso that the water flows along the length of the UV-lamps 6 and thephotocatalyst carriers 7 and is in contact with the photocatalystcarriers 7 for as long a period of time as possible.

The UV-lamps 6 are each connected to the power source unit 10 and canemit radiation with a spectrum ranging from 180 to 400 nm, which isirradiated onto the adjacent photocatalyst carrier 7. The UV-lamps 6 areeach formed of a double silica glass tube with the outer tube serving asa jacket to protect the light-emitting element inside from the water.

The photocatalyst carriers 7 may be made of materials such as noblemetals, titanium dioxide, aluminum oxide, silicon oxide, and mixturesthereof. Of these, titanium dioxide is particularly preferred for use asthe material of the photocatalyst carriers 7.

While three UV-lamps 6 and two photocatalyst carriers 7 are arranged inthe embodiment shown, the UV-lamps 6 and the photocatalyst carriers 7may be provided in any number that can emit sufficient radiation intothe water. The number of the UV-lamps 6 and the photocatalyst carriers 7may vary depending on the performance of individual UV-lamps 6 andphotocatalyst carriers 7, the amount of water processed per unit lengthof time, types and amounts of organic materials to be decomposed andother conditions.

While the water 100 to be processed by the photocatalyticwater-processing system 1 in this embodiment is industrial circulatingwater, the photocatalytic water-processing system 1 can process othertypes of water, including industrial waste water, tap water, sewage,soil water and underground water, pond water, swimming pool water, anddomestic waste water.

While in FIG. 1, the pump 4 and the electrode unit 3 of thephotocatalytic water-processing system 1 are integrated into thereservoir 11 for use in a cooling tower used in industrial plants forcooling industrial circulating water, these units may be used, for thepurpose of removing organic and inorganic materials, in reservoirsintended for the preprocessing of industrial waste water or sewagewater, in tap water tanks for the maintenance purpose, or in any otherplaces where water is stored.

According to the present embodiment, the main unit 2, the pump 4, andthe electrode unit 3 are provided as individual units. This constructionallows a small and lightweight design of the main unit 2, leading tocost reduction.

(Details of Electrode Unit)

Referring now to FIG. 2, the construction and operation of the electrodeunit 3 are described. FIG. 2 is a diagram of an electric circuitrepresenting the electrode unit 3 of the photocatalytic water-processingsystem 1. The electrode unit 3 is shown stripped of the electrode cover30.

The electrode unit 3 of the photocatalytic water-processing system 1includes a circuit comprising at least a pair of electrodes 3A and 3B,the above-described electrode cover 30, a DC power source 31 that formsa part of the power source unit 10 of FIG. 1 and supplies current to theelectrodes 3A and 3B, a resistor 32 connected to one of poles of the DCpower source 31 and the electrodes, a resistor 33 connected to the otherpole, and a capacitor 34 connected between the electrodes 3A and 3B. Inthe example shown in FIG. 2, the positive pole of the DC power source 31is connected to the electrode 3A via the resistor 32 and one end of thecapacitor 34, and the negative pole of the DC power source 31 isconnected to the electrode 3B via the resistor 33 and the other end ofthe capacitor 34.

The DC power source 31 includes a flow control dial arranged on thecontrol panel. By turning the dial, the output voltage of the DC powersource 31 can be adjusted between 10 V to 50 V depending on the type anduse of the water to be processed. Also, the DC voltage applied to theelectrodes 3A and 3B can be adjusted by varying the resistance of theresistors 32 and 33.

The principle of the processing of the water 100 by the electrode unit 3is now described.

In the photocatalytic water-processing system 1, the electrolysis of thewater 100 is initiated upon application of a voltage of 10 V to 50 V tothe pair of electrodes 3A and 3B of the electrode unit 3, which isinserted in the reservoir 11 filled with the water 100. A few minutesafter application of voltage, small bubbles are generated in the water100. In the photocatalytic water-processing system 1, the rust and scaledeposits formed in the reservoir 11 come off (erosion effect), andflocculate and precipitate as these small bubbles collide with thedeposits.

Since these deposits are known to provide a major breeding ground ofbacteria, the electrolysis by the electrode unit 3 of the photocatalyticwater-processing system 1 plays a supportive role for the photocatalyticwater-processing by reducing the amount of the deposits.

Thus, in the present embodiment the electrode unit 3 provided in thephotocatalytic water-processing system for electrolysis serves as asupportive or alternative sterilizing means to eradicate bacteria whenthere are too many bacteria to be eliminated by the photocatalystprocessing alone or when the UV-lamps fail or need maintenance.

In addition, the electrolysis provided by the electrode unit 3 of thephotocatalytic water-processing system 1 prevents the deposition of themetal rust on the surface of the reservoir 11 or various pipes or on thejacket of the UV-lamps 6 and causes the scale of calcium and magnesiumto dissolve and come off the surface, and flocculate and precipitate.Furthermore, the resulting increase in the amount of dissolved oxygenprevents deposition of algae and water rotting by bacteria. Also,hypochlorous acid generated during the electrolysis of the watereffectively kills bacteria such as Legionella and E. coli. As described,the processing of water by the photocatalytic water-processing system 1does not involve any chemicals and, thus, only requires low-cost setup.

As the water 100 is subjected to electrolysis by the electrode unit 3 ofthe photocatalytic water-processing system 1 for a prolonged period oftime, the scale mainly composed of calcium, magnesium, potassium orsodium present in the water 100 that flows between the electrodes 3A and3B flocculates and precipitates. Thus, the initially turbid water 100becomes clear over time during the extended electrolysis. This resultsin an increased transmittance of the radiation emitted by the UV-lamps 6and thus ensures effective sterilization.

Our study showed that the oxidation-reduction potential of water 100 wasdecreased from +151 mV to +118 mV during a 55-day-long continuouselectrolysis process. The water 100 after the processing in thephotocatalytic water-processing system 1 had the amount of dissolvedoxygen increased by approximately 10% and had an approximately 30%conductivity as compared to the initial conductivity of the water. Thestudy also indicated that the amount of oxygen dissolved in theprocessed water increased as the oxidation-reduction potential wasdecreased.

In summary, the elimination of inorganic compounds by the electrolysisperformed by the photocatalytic water-processing system 1 of the presentinvention offers the following advantages:

(1) Crystallization of inorganic compounds (scale) is prevented becauseof the increased ionization and precipitation of the compounds: cloggingof the pipes by the calcium or magnesium scale is prevented and water iseffectively softened as a result of increased precipitation.

(2) Growth of iron bacteria is prevented by the suppression of oxidationof water (reduction).

(3) The generated oxidizing or reducing agents facilitate the waterprocessing.

(4) Formation of the scale deposition on the jacket of UV-lamps 6 isprevented by the preventing action against the crystallization of scaleand, as a result, the life of UV-lamps 6 is extended.

(Operation of the Entire Photocatalytic Water-Processing System)

The operation of the entire photocatalytic water-processing system 1 inthe water processing is now described, along with the associated changesin the water.

In the initial state, the electrode unit 3 and the pump 4 are placedwithin the reservoir 11 and the main unit 2 is in fluid communicationwith the reservoir 11. The electrode unit 3, the pump 4, and theUV-lamps 6 are activated by turning on the switch of the power sourceunit 10 arranged on the control panel as described above.

The pump 4 operates to suction the water 100 from the reservoir 11 andforce it through the inlet pipe 8 into the inlet side 101 of the mainunit 2.

Once activated, the electrode unit 3 starts electrolysis of the water100 as a 10 V to 50 V voltage is applied to the pair of electrodes 3Aand 3B. Activated, the UV-lamps 6 emits radiation with a spectrumranging from 180 to 400 nm, which is irradiated onto the set ofphotocatalyst carriers 7 arranged opposed to one another.

In brief, through the operation of the photocatalytic water-processingsystem 1, the water 100 is sequentially subjected to the electrolysis bythe electrode unit 3, filtration by the filter 5, and photocatalyticprocessing by the photocatalyst carriers 7 and the UV-lamps 6. As aresult, the inorganic compounds present in the water 100 areprecipitated in the reservoir 11. The precipitates are then removedmanually.

During the operation of the photocatalytic water-processing system 1,the water 100 is forced out of the reservoir 11 by the pump 4 and, asindicated by the arrows in FIG. 1, flows through the inlet pipe 8 intothe main unit 2, and then out of the main unit 2 through the outlet pipe9, and returns back into the reservoir 11. The water 100 is thensupplied via the water outlet 13 into the in-plant circulation pathwhere it is used for industrial purpose. The used water 100 is thenreturned to the reservoir 11 via the water inlet 12.

The water 100 circulates through the in-plant circulation path duringthe operation of the plant. Even when the water 100 is not supplied intothe in-plant circulation path, the water can be processed by circulatingit through the circulation path between the reservoir 11 and the mainunit 2.

As the water 100 circulates through the in-plant circulation path, thephotocatalytic water-processing system 1 operates to decompose andremove organic and inorganic materials present in the water 100temporarily stored in the reservoir 11. Specifically, this is done inthe following manner.

As a DC current is applied to the electrodes 3A and 3B of the electrodeunit 3 in the photocatalytic water-processing system 1, the water 100 iselectrolyzed by the electrodes. The electrochemical reaction that takesplace between the pair of electrodes 3A and 3B causes formation ofbubbles, which collide with the rust and inorganic scale deposits ofsilica and magnesium formed in the piping of the reservoir 11,dissolving the deposits and causing them to come off the surface of thepiping. The inorganic scale that has been dissolved and come off thesurface flocculates and precipitates in the reservoir 11 and is keptfrom crystallizing.

The water 100 sent to the main unit 2 via the inlet pipe 8 is thenfiltered as it passes through the filter 5 in the main unit 2. Thisremoves solid materials and organic materials suspended in the water.

Subsequently, as the water 100 passes through the area where a set ofUV-lamps 6 and a set of photocatalyst carriers 7 are arranged, thephotocatalytic process is carried out. The UV-lamps 6 are each capableof emitting radiation with a spectrum ranging from 180 to 400 nm, andthe photocatalyst carriers 7 are made of such materials as titaniumdioxide to receive the radiation emitted by the UV-lamps 6.Specifically, the following photocatalytic process is done.

Upon irradiation of the photocatalyst carriers 7 with the radiationemitted by the UV-lamps 6, the valence electrons present at the surfaceof the photocatalyst carriers 7 are excited and move to the conductionband, leaving holes in the valence band. The electrons and the holes ofthe photocatalyst carriers 7 act upon the dissolved oxygen and water 100to generate two forms of active oxygen capable of decomposition:superoxide ion and hydroxide radical, together with hydrophilic —OHgroups.

The water 100 filtered by the filter 5 then chemically reacts with thetwo active oxygens and hydrophilic —OH groups. As a result, most oforganic compounds present in the water 100 are decomposed into carbondioxide and water, and inorganic contaminants present in the water 100,such as NOX and SOX, are oxidized into nitric acid and sulfuric acid.Other inorganic materials precipitate to the bottom of the main unit 2.

The water processed in the main unit 2 is then returned to the reservoir11 and is repeatedly circulated through this circulation path while themain unit 2 is in operation. In this manner, the above-describedelectrolysis and photocatalytic process are continuously carried out.Solid materials in the processed water 100 can be readily separated assediments, so that the resulting supernatant in the reservoir 11 can berecycled.

The decomposition of organic compounds, bacteria and other harmfulmaterials by the photocatalytic reaction carried out by thephotocatalytic water-processing system 1 offers the followingadvantages:

(1) Sterilization

Harmful bacteria, including genus Legionella, E. coli, Staphylococcusaureus, and Pseudomonas, can be eradicated.

(2) Prevention of Algae Growth

The growth of algae can be prevented since the spores are decomposed inthe photocatalytic reaction.

(3) Eradication of Microbes

Microorganisms can be eradicated by the photooxidative effect of thephotocatalytic reaction.

(4) Decomposition of Organic Materials

Organochlorines such as trihalomethane are decomposed.

The photocatalytic water-processing system 1 can be used in other fieldswhere water processing is required and can effectively eliminate organiccompounds, inorganic compounds, and contaminants and kill microbeswithout using any chemicals.

The photocatalytic water-processing system 1 of the embodiment, whichcombines electrolysis with photocatalytic processing, can preventformation of rust and scale deposits on the electrodes 3A and 3B,photocatalyst carriers 7, and the jackets of UV-lamps 6, so that theelectrolytic performance of the electrodes 3A and 3B can be maintainedfor an extended period of time, as can the photocatalytic performance ofthe photocatalyst carriers 7 and the UV-lamps 6.

The photocatalytic water-processing system 1 in which inorganic andorganic materials are precipitated in the reservoir 11 or the main unit2 requires only occasional cleaning and is easy-maintenance.

The photocatalytic water-processing system 1 does not produce harmfulby-products resulting from the use of chemicals or cleaners and thus hasa longer life while requiring less maintenance.

Not requiring use of chemicals or cleaners, the photocatalyticwater-processing system 1 does not require reaction tanks in which tocarry out chemical processes. In addition, the construction in which themain unit 2, the pump 4, and the electrode unit 3 are provided asseparate units allows a small and lightweight design of the main unit 2,leading to cost reduction.

EXAMPLES

The present invention will now be described with reference to anexemplary experiment, which is not intended to limit the scope of theinvention in any way.

In this experiment, the water 100 to be processed is industrialcirculation water (tap water) and the reservoir 11 used was a 10-tonopen cooling tower. The water temperature in the cooling tower was 25°C. during water processing. The electrodes 3A and 3B of the electrodeunit 3 were each a 4 cm×20 cm platinum-plated expanded titanium alloyplate. A 16V DC voltage was applied to the electrodes 3A and 3B for thewater processing. The pump 4 was an inverter-controlled 0.75 kw pumpmanufactured by Hitachi, Ltd. The filter 5 was a 140-mesh polypropylenefabric. Two 14W low-pressure mercury lamps that emit radiation with awavelength of 254 nm were used as the UV-lamps 6. The photocatalystcarriers 7 were each an expanded titanium dioxide piece.

In this experiment, a photocatalytic water-processing system 1 havingthe above-described construction (referred to as the presentexperimental system, hereinafter) is used to process cooling tower water(tap water) for 85 consecutive days and the number of Legionella in thewater was counted prior to and during the processing. The results areshown in Table 1.

TABLE 1 Day Test Results 0 4.0 × 10² CFU/100 ml 50 1.0 × 10² CFU/100 ml66 Undetected 85 Undetected CFU: (colony forming unit)

As can be seen from the results of Table 1, the initial Legionella countwas 4.0×10² CFU/100 ml, which was reduced to one-fourth the initialcount (1.0×10² CFU/100 ml) by day 50 using the present experimentalsystem. No Legionella bacteria were detected after day 66.

We also measured the pH, conductivity, oxidation-reduction potential,turbidity, calcium hardness, and chloride ion level in the cooling towerwater during the processing test using the present experimental system.The results are shown in Table 2.

TABLE 2 Oxidation- Cunductivity reduction Turbidity Calcium hardnessChloride ion Day pH (mS/m) potential (mV) (NTU) (mgCaCO3/L) (mgCl⁻/L) 08.3 87 151 36 42.5 97 7 8.25 65 144 22 52.43 120 17 8.25 48 140 20 59.9358 27 8.22 48 139 12 69.92 54 35 8.11 32 136 2 85.2 24 41 8.14 31 128 292.39 21 49 8.22 42 125 1 107.37 41 55 8.11 27 118 0 104.9 25 *NTU(Nephelometric Turbidity Unit) is a measure of turbidity determined byelectric equipment such as a photoelectric cell, as the amount of lightscattered perpendicular to the incident light.

As can be seen from the results of Table 2, the oxidation-reductionpotential decreased over the course of the processing using the presentexperimental system, as did the turbidity and the chloride ion level.Conversely, the calcium hardness increased.

The results demonstrate that the scale deposits formed on the surface ofthe inner wall of various pipes loosened and came off as theoxidation-reduction potential of the water was decreased and the scalewas thereby reduced. It has also been shown that rust was also removedas the inner wall was progressively reduced.

The oxidation-reduction potential was decreased from the initial valueof +151 mV down to +118 mV on day 55 by using platinum-plated titaniumalloy, a metal material known to significantly decreaseoxidation-reduction potential, as the material of the electrodes 3A and3B of the present experimental system.

It has been demonstrated that during the electrolysis by the presentexperimental system, a DC current flows through, and therebyelectrolyze, the water that passes the electrode unit 3. As a result,the oxidation-reduction potential of the water is decreased. Thedecrease in the oxidation-reduction potential of the water in turnbrings about electron reactions (e.g., formation of ion bonds andcovalent bonds) and photocatalytic chemical reactions involving organiccompounds present in the water, decomposing the organic compounds.

Because of its relatively low oxidation-reduction potential, themolecules of the water processed in the present experiment are stronglybonded together by electron bonds. Such water hardly oxidizes othersubstances and is thus favorable to living systems. The presentexperimental system has also been proven to activate water and enhancethe washing power that water has by nature. As used herein, the term“washing power” refers to the ability of water to dissolve matters. Atype of water with a higher washing power can dissolve and suspend adissolved matter for a longer period of time. The present experimentalsystem enhanced the inherent washing power of water and thussuccessfully removed and dissolved the rust and scale deposits formed onthe inner wall of the pipes.

In the present experimental system, the electrolysis by the electrodeunit 3 removes calcium and magnesium in the reservoir 11 before water issubjected to the photocatalytic processing. This prevents deposition ofthese compounds onto the jacket of the UV-lamps 6. Thus, the presentsystem has made it possible to substantially remove rust and inorganicscale deposits of calcium and magnesium formed on the jacket of UV-lampsor in the pipes or reservoirs, which cannot be removed in theconventional photocatalytic water-processing systems. Accordingly, thepresent system allows highly effective water-processing.

Furthermore, the results of the present experiment showed that some ofthe organic compounds were evaporated and the rest of the compoundsprecipitated to the bottom of the main unit 2. This suggests that thesupernatant resulting from the processing by the present experimentalsystem can be recycled for industrial use.

In addition, the advantageous effects of the present experimental systemare highly reproducible and sustainable and hardly diminish over time.Also, the present experimental system does not use chemicals and otherexpendable supplies, so that its running cost consists of electricitycost alone. Specifically, the cost associated with the introduction ofthe present system was recovered in one year to one and half a year.

INDUSTRIAL APPLICABILITY

As set forth, the present invention provides a photocatalyticwater-processing system that enables unprecedented water-processing inwhich rust and scale deposits of silica, magnesium and other inorganiccompounds formed in the reservoir, in which to store water that requiresprocessing (e.g., industrial circulating water), or in the piping, or onthe jacket of the UV-lamp of the system, are dissolved and removedwithout using any chemicals.

1. A photocatalytic water-processing system for decomposing organic andinorganic materials present in water, the system comprising: a reservoirfor storing the water to be processed, said reservoir having anelectrode unit therein for electrolyzing the water so as to flocculateand precipitate the inorganic materials in the reservoir; a main unitformed separately from the reservoir and connected to the reservoir; aninlet pipe connecting the reservoir and the main unit for guiding thewater from the reservoir to the main unit; an outlet pipe connecting themain unit and the reservoir for returning the water to the reservoir; apump for guiding the water from the reservoir to the main unit throughthe inlet pipe and retuning the water from the main unit to thereservoir through the outlet pipe; a filter arranged within the mainunit; and photocatalytic processing means arranged within the main unitat a downstream side of the filter, said photocatalytic processing meansincluding a photocatalyst carrier and a UV-lamp so as to decompose theorganic material in absence of scale formed of the inorganic materials.2. The photocatalytic water-processing system according to claim 1,wherein the electrode unit includes at least two electrodes formed of atleast one of zinc, a magnesium alloy, copper, iron, stainless steel, atitanium alloy, an aluminum alloy, and platinum.
 3. The photocatalyticwater-processing system according to claim 2, wherein the electrode unitcomprises a platinum-plated titanium alloy.
 4. The photocatalyticwater-processing system according to claim 1, wherein the filtercomprises any one of porous oxide ceramics, aluminum oxide, syntheticresin fiber, paper, stainless steel, and activated carbon.
 5. Thephotocatalytic water-processing system according to claim 1, wherein theUV-lamp is configured to emit radiation with a spectrum ranging from 180to 400 nm.
 6. The photocatalytic water-processing system according toclaim 1, wherein the photocatalyst carrier comprises any one of noblemetal, titanium dioxide, aluminum oxide, silicon oxide, and a mixturethereof.
 7. The photocatalytic water-processing system according toclaim 1, wherein the water to be processed comprises at least oneselected from industrial circulating water, industrial waste water, tapwater, sewage, soil water and underground water, pond water, swimmingpool water, and domestic waste water.
 8. The photocatalyticwater-processing system according to claim 1, further comprising a wateroutlet provided to the reservoir so as to eject supernatant forrecycling the water.
 9. The photocatalytic water-processing systemaccording to claim 1, wherein the pump is configured to guide at leastpart of water treated at the main unit further into the main unitthrough the inlet pipe.
 10. The photocatalytic water-processing systemaccording to claim 1, further comprising a power source unit forproviding power to the electrode unit, the pump, and the UV-lamp, eachof said main unit, the pump, the electrode unit, and the power sourceunit being independently formed.